Most conventional computed tomography (CT) systems use a detector that includes a scintillator and a photodiode array. The scintillator converts x-ray photons into photons of visible light and the photodiode array converts the photon of visible light into an electric signal current. The integrated charge of the electric signal current produced by the photodiode array is proportional to the energy of the x-ray photon captured by the scintillator.
Typically, the photodiode array used in a computed tomography detector includes a plurality of photodiode elements in an arrangement such as 16×16, 16×32, 16×64, and 24×64. The photodiode array is typically coupled to a scintillator array. Each photodiode element of the photodiode array is generally about 1 mm wide and 1 mm long. This typically results in a capacitance in the range of approximately 10 pF to 15 pF per photodiode element.
In order to produce images with high temporal resolution, there is a constant pressure to increase the speed at which a CT system acquires data. Additionally, in the interest of patient safety, there is a desire to reduce the amount of x-ray photons needed to produce a clinically useful image. Reducing the noise produced by the detector may help to both increase the speed of acquisition and lower the x-ray dose needed to produce a satisfactory image. One of the significant contributors to image noise is the electronic noise generated by the detector. One way to reduce the electronic noise contributed by the detector is to reduce the capacitance of each photodiode element in the photodiode array.
Thus, in order to reduce electronic noise, there is a need to develop a lower capacitance photodiode element and a lower capacitance photodiode array without compromising the response time of each photodiode element.